Unmanned aerial vehicles (UAVs) provide a useful means to aerially explore locations that are unsuitable for manned aircraft, for example because the area is considered too unsafe to allow human access, or because the area is in a confined space that is too small to accommodate a manned aircraft. UAVs may for example be equipped with a sensor device, such as a camera, to feed information back to a remotely-located user. An advantage of UAVs, as compared to remotely controlled ground vehicles for example, is their ability to fly over and around obstacles.
A common use for UAVs is in search and rescue operations. In particular, UAVs are useful for determining whether or not it is safe to allow rescue personnel to enter an area, and indeed whether or not there are people or animals in an area that require assistance. Sites where search and rescue UAVs are used may be strewn with obstacles, and may often only be accessible through small openings. For example, it may be that a UAV is used to examine the inside of a collapsed building in order to determine the location of survivors and to find the safest access route for rescuers.
In order to be useful in such challenging environments it is desirable for UAVs to be highly manoeuvrable and have high stability in flight. UAVs in the form of helicopters are particularly useful in search and rescue applications because of their ability to hover. Often, UAVs are multi-rotor helicopters, comprising for example four or more rotors to improve flight stability. Helicopter UAVs comprising four rotors are sometimes referred to as ‘quadcopters.’
A common quadcopter design has a co-planar arrangement of rotors, which arrangement provides good stability. Quadcopters having coplanar rotors are manoeuvred forwards, backwards or sideways (i.e. in the x or y direction) by altering the rotational speed of each rotor. A disadvantage of such a design is the difficulty of manoeuvring the UAV in the x or y direction without substantial vertical movement (i.e. in the z direction).
Another typical quadcopter design comprises a so-called ‘v-tail’ arrangement of rotors, in which two rotors are coplanar, whilst the remaining two are angled at 45 degrees to the co-planar rotors and at 90 degrees to each other (forming a ‘v’ shape). Such an arrangement improves manoeuvrability, but does not completely eliminate the difficulty of achieving horizontal-only movement.
Rotor-based UAVs sometime incorporate moveable wings or other moveable aerodynamic surfaces in order to improve manoeuvrability but incorporating such extra moveable surfaces increased the number of moving parts in the UAV and can add weight/complexity and/or reduce reliability as a result.
Conventionally, multi-rotor UAV helicopters are elongate in shape, extending further in the x and y directions than in the z direction, with rotors spaced apart horizontally. Often, rotors are mounted on booms connected to a central body. Such an arrangement leaves rotors vulnerable to damage if the UAV comes into contact with an obstacle whilst in flight. Although it is known to enclose rotors in a protective cowling, the power-to-weight ratio of the resulting UAV is diminished.
Typically, sensors such as cameras or other scanning equipment is mounted underneath UAV helicopters away from top-mounted rotors. A disadvantage of that arrangement is the inability of the UAV to scan its entire surrounding, including the space above it. When UAVs are used to explore and map an area, such as the inside of a damaged or partially collapsed building, it would be useful to map the entire volume of a space.
A further disadvantage of conventional, elongate multi-rotor UAV helicopter designs is their susceptibility to instability in unpredictable and turbulent airflow. In particular, both coplanar and v-tail quadcopters do not cope well when buffeted with air currents from different directions, and suffer from reduced stability when flying in close proximity to objects such as walls or beams that disturb local air flow. Furthermore, if a collision with an object unbalances known UAVs, it is typically very difficult for an operator to maintain flight. If, for example, a collision leads to a conventional UAV landing the wrong way up, take-off is unlikely to be possible, even if the crash did not result in severe damage.
A drawback of traditional, elongate multi-rotor UAV helicopters is that should one or more rotors be damaged or become inoperable during use, continued flight of the unbalanced UAV can be extremely difficult or impossible. Since UAVs are often deployed in areas not deemed safe for human access, it is unlikely that retrieval of the UAV will be possible, and so the equipment will be lost.
Therefore, there remains a need for highly manoeuvrable UAVs with stable flight and the ability to scan their surroundings in all directions with on-board sensors. There also remains a need for UAVs that are more robust and resilient to crash damage, and that can continue to fly in the event of damage during use.
The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved UAV. Alternatively or additionally, the present invention seeks to provide an improved method of flying a UAV for the purposes of acquiring information about the surrounding environment from sensors on the UAV.